The invention relates to a method for transmitting power and data in a bus system for occupant protection devices in vehicles. The invention also relates to a control module for performing the method.
Methods and devices for performing such methods are known from German Patent Publications DE 44 41 184, DE 196 43 013, and DE 197 51 910. The respective goal is to safeguard the safety relevant peripheral control modules against short duration disturbances, for example interruptions or overloads of the d.c. voltage from a bus system required for the power supply. Furthermore, in the conventional methods, digital data are transmitted over the same conductor section, with the power supply, by voltage modulation of the d.c. voltage. U.S. Pat. No. 4,736,367 and a Motorola Semiconductor Application Note AN475/D by Burri/Renard: xe2x80x9cSingle Wire MI Bus controlling stepper motorsxe2x80x9d, 1993, also disclose d.c. voltage modulated data transmission.
The special problem of current loading of the bus system during simultaneous transmission of power and data has been described particularly in German Patent Publications DE 196 43 013 and DE 197 51 910. Thus, there is the risk that it will be impossible to process the data.
For example, in bus systems in motor vehicles, direct current or d.c. voltage is usually used for the power supply, onto which the data can be modulated. Due to an excessively high current consumption or other factors that act upon the d.c. voltage, the data modulated onto the d.c. voltage can become unrecognizable.
The data transmission, particularly for safety relevant bus systems for power and data transmission with several control modules arranged within the bus system, which modules are also to be triggered sequentially, must not be jeopardized, for example, by an ignition of initial occupant protection devices. For this purpose methods for providing extra energy are described in addition to the energy storage (autarchic capacitors) provided in the peripheral control modules. This extra energy may, for example, be needed for igniting the occupant protection devices. These methods provide the extra energy in a way that does not load the bus system. Thus, the energy storage devices are preferably charged in the transmission pauses or are charged with very low current consumption from the bus system.
A problem with the above methods is seen in that the energy storage devices are severely discharged when an occupant protection device is triggered and consequently a recharging from the bus system starts directly thereafter. Even with current limit circuits that are provided, this recharging can result in a high load on the data transmission system when several occupant protection devices are triggered simultaneously and therefore their energy storage devices must be recharged. It is then possible that control modules of occupant protection systems that are triggered later cannot be timely triggered again at the right time, or possibly interrogation routines to be made cannot be carried out.
Heretofore, only the resistance check in a pyrotechnical igniter of an occupant protection device is known as a method for verifying an executed triggering subsequent to a trigger command. An intact, not yet triggered pyrotechnical igniter has a low resistance. When the pyrotechnical igniter triggers, the ignition wire is either interrupted or in individual cases, can also be short-circuited. A check can therefore be faulty. In addition, the verification is not applicable for other ignition concepts, for example with cold gas generators.
For the above reasons, it is an object of the invention to provide a method of the above described type wherein an additional load on the bus system subsequent to triggering of individual occupant protection devices can effectively be avoided. In addition, a method for verifying an executed triggering subsequent to a trigger command is shown. This method is based on one of the preceding methods, is very simple and can be reliably implemented. Furthermore, a control module for implementing the method is indicated.
According to the invention energy and data are transmitted through a bus system in an occupant protection system including a central processing unit (7), triggerable occupant protection devices (1.1) communicatively connected through control modules (6) and through said bus system (5) to said central processing unit (7), wherein the following steps are performed:
(a) transmitting data and energy between said central processing unit and said control modules through said bus system,
(b) providing a respective energy storage device for each respective control module of said control modules,
(c) charging said respective energy storage device through said bus system for a limited time to assure proper operation of said respective control module and of an occupant protection device connected to said respective control module,
(d) normally maintaining a charged state of said respective energy storage device, and
(e) interrupting said charging and maintaining of the energy storage device of the respective control module in response to an executed triggering of a respective occupant protection device.
An essential feature of the invention is that the charging or recharging of the energy storage device of the already triggered occupant protection devices and/or of the corresponding control modules is interrupted. In this way, the bus system can continue to transmit the digital data undisturbed and the control modules of the occupant protection devices that have not yet been triggered can receive their data. This interruption or suppression can be realized in a particularly safe way and free of loss by high-resistance separation. It is particularly preferable to interrupt the recharging at least until a reset command. The reset command resets the peripheral control modules again and then begins with the recharging of their energy storage devices. The energy available in the energy storage device of an occupant protection device, after the device has been triggered, can be used advantageously for checking and recognizing a successful triggering. If, for example because of a break in the conductor to the igniter of the occupant protection device, the device cannot be triggered, then the energy does not flow from the energy store. This situation can be recognized by a comparison with a rated value and can be displayed or other measures can be taken.
According to the invention there is also provided a control module for an occupant protection system including a central processing unit, triggerable occupant protection devices communicatively connected through control modules and through said bus system to said central processing unit, said control module comprising a switch normally connecting an energy storage device to said bus system for charging said energy storage device through said bus system, a control signal generator operatively connected to said bus system for receiving a trigger signal, said control signal generator having a control output connected to said switch for interrupting said switch after said trigger signal has been received by said control signal generator.